Power spectrum of long-period solar oscillations and 160-min pulsations during 1974–82

Abstract

We report here the results of solar oscillation observations carried out between 1974 and 1982 using the Crimean solar magnetograph. We have eliminated all peaks of telluric origin from the mean power spectrum; of the remaining 32 dominant (≥2σ) peaks, 19 are of solar origin and 13 are partly blended with the atmospheric peaks. We found that 10 solar peaks are in very good agreement with the modes g₁₀–g₂₀ of degree 1 = 4 calculated by Christensen-Dalsgaard et al.¹ for the solar model C with the envelope enriched in heavy elements by accretion. Deviations of the observed long-period oscillations from a linearity can be appreciable, leading to the appearance of combination frequencies. The dominant 160-min peak seems to be excited by a strong ‘double’ resonance of 2g₈ mode of model C with a combination frequency, and two other combination frequencies of modes 1g₁ and 2f including the unstable mode l = 1. As model C is also in good agreement with the neutrino experiment, we suggest that this could be considered as the most appropriate model of the Sun. In contrast to previous detailed studies of solar pulsation with the particular 160.01-min period^2,3, the emphasis here is on the search for other possible long-period solar oscillations of low degree. These oscillations are thought to be bound to the regions beneath the convection zone and penetrate to the Sun's core which makes them a powerful tool for analysing the solar internal structure and the evolution of the Sun.